1. Field of the Invention
The present invention relates to a latent image projecting mirror surface body and, more particularly, to a latent image projecting mirror surface body which can be utilized as one for recognition of secret codes or one for ornamentation of gadgets or articles.
2. Statement of the Related Art
There has conventionally been a classical magic mirror, as a mirror surface body similar to a latent image projecting mirror surface body. This magic mirror is based upon such a phenomenon that images for example which are deeply sculptured in its back surface so as to form protrusions give convexities and concavities on its front mirror surface when the same is polished, and that such images are reflected in the reflected light.
The principle of the above-mentioned magic mirror will hereinafter be described with reference to the drawings.
FIG. 1 schematically shows a mirror surface body which has been subjected to a magic mirror process, wherein a light beam from a small light source 11 is projected through a pin hole 12 onto a mirror-polished substrate 13 where a shallow and wide recess 15 exists which recess 15 is produced on the front surface of the mirror surface body after polishing, and to the back surface of the body is formed therein with a sculpture 132. If there is no recess or protrusion or stain on the surface, then evenly distributed rays are reflected on the screen 14 thereby forming a simple even-brightness image of the corresponding shape to the mirror surface 131. However, since the shallow and moderate recess 15 exists on the surface 131, the recess part serves as a concave mirror which converses light, and reflects rays as shown by the dotted lines 16. Therefore, the light image formed on the screen 14 has non-uniform distribution of brightness as shown by a curve 17. That is, in general the light image on the screen 14 has a bright spot or bright region when the mirror face has a concave defect, and a dark spot or dark area when the mirror face has a convex defect. When the surface has parallel recess-shaped unevenness, the light image becomes a parallel shadow pattern, and one can detect such a shallow excess of 0.3 .mu.m depth and 1 to 3 mm size.
In the above conventional example, the substrate 13 having its back surface formed therein with a protruded sculpture 132 must be polished on its front surface 131 into a mirror surface. Accordingly, a large amounts of time and expenditure is necessary for the formation of the images as well as for the conversion into the mirror surface.
Meanwhile, various methods for readily observing the latent images in the front surface of the substrate are known and have hitherto been proposed (for example Japanese Laid-Open Utility Model 57-134612, Japanese Laid-Open Patent 57-186106). In this case, however, nicked marks and the like on the substrate are formed in the front surface thereof for reading, so that such visible marks do not become secret codes on account of their visibility. In addition, because the marks and the like exist on the front surface, damages are caused to the front surface in view of an aesthetic appearance thereof. This imposes a limitation upon the use of the mirror surface bodies based on the above methods.